A single center study of patients with thyroid disease studied before and after treatment, as well as 10 normal controls. Metabolic energy expenditure, exercise capacity and cardiovascular function will be evaluated in overt hyperthyroidism, subclinical hyperthyroidism, overt primary hypothyroidism, subclinical hypothyroidism and normal controls. Tissue specific effects will be evaluated in the treatment of patients with overt hypothyroidism using levothyroxine (LT4) to normalize TSH and 3,5,3' - trithyroacetic acid (Triac) to normalize TSH.